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mixture is heated in a paraffin or metal-bath to 150— 1 60° for
8 hours. The dark coloured mass is poured whilst hot into a
large basin containing about a litre of cold water, and boiled
for an hour. The unattacked anthraquinone, which does not
dissolve, is removed by filtration at the pump. The precipitate
is then replaced in the basin and boiled up again with about
\ litre of water, filtered and finally washed once or twice with
boiling water. The combined filtrate and washings, which hayc
a deep brown colour, are evaporated with the addition of 0*2 gram
of potassium chlorate until about vr litre of liquid remains. It
is now nearly neutralised with sodium carbonate solution (about
i 20 grains soda crystals) but not completely, as the sodium s,alt
of the monosulphonic acid is less soluble in presence of acid.
It is therefore convenient to pour out half a .test-tube of the
acid liquid, and proceed to neutralise the remainder. The small
quantity of acid liquid is then replaced. The liquid is evapo-
rated on the water-bath until a scum covers the surface, and it
is then left to cool. The sodium salt of the sulphonic acid
crystallises in pale yellow, silky crystals, and is separated at the
pump. After being washed three or four times with a very little
slightly acid water, it is dried on a porous plate. Yield, 20 — 25
*. grains. A further quantity of the salt may be obtained by
evaporating the mother-liquor, but it is liable to contain sodium
Properties. — The sodium salt of the sulphonic acid crystal-
lises, when pure, in colourless leaflets, slightly soluble in cold
water, insoluble in alcohol.
<v • n ir /COX- u /OH a
Alizarin, ^ C(iH-OH
Graebe, Licbermann, Annalcn.Spl^ 1869, 300; Perkin, Engl
Patent, 1869, No. 1948; A. G. Perkin. Private communi-
20 grins, anthraquinone monosulphonate of sodium.
90 „ caustic soda.
5 „ potassium chlorate.